Monitors have come a long way since they
were coupled with computers in the 1970’s. IBM introduced
their first color monitor back in 1981; it could render 4
colors with a maximum resolution of 320 x 200. The next
progression was EGA, which allowed up to 16 colors back in
1984. From there we had VGA, UVGA, and the still popular
UXGA which can support resolutions of up to 1600 x 1200, and
over 16 millions colors. Another big leap in technology was
the introduction of multi-scan monitors, which gave the end
user the ability to change resolutions and frequencies on
the fly. Traditional monitors used analog displays, which
meant the digital signal coming from the graphics card had
to be translated to an analog signal in order for the
monitor to work. This technology also takes up more space,
due to the fact that the picture is “beamed” onto the
screen. In order for the beam to fully extend, it needs to
be a certain distance from the display. A good example of
this would be a projector. The further the projector is
positioned from the wall, the larger the picture.
LCD technology started back in 1888,
invented by an Austrian called Friedrich Reinitzer. He
melted cholesteryl benzoate, and let it cool. Upon cooling,
he noticed that the liquid turned blue before finally
crystallizing. The then crude discovery had no use as of
yet, up until RCA made the first experimental LCD back in
1968.
One advantage of using LCD technology is
the fact that the signal always stays digital, which means
the signal is cleaner. Power consumption is also drastically
lower. While the typical CRT monitor consumes 110 watts, LCD
monitors consume 30-40 watts on average. The monitor can be
sometimes the largest consumption device of a computer
workstation, and typically attributes to 80% usage of the
systems electricity. Not to sound repetitive, but the size
reduction is probably the biggest draw. Because we no longer
need the light beam, monitor size can be dramatically
smaller.
The term LCD refers to liquid crystal
display. An LCD contains tiny liquid crystals, and there are
several different types. These crystals react to changes in
voltage, and twist according. Depending on the angle, they
allow light emitted from behind them to surface. The
crystals do not have the ability to create the light
themselves, so computer monitors have built in florescent
tubes located in different areas which direct light beams to
the crystals.
There are two types of LCD monitors:
Passive Matrix and Active Matrix, the later being the most
common type because of speed. Active Matrix displays use
TFT’s (thin filmed resistors). TFT’s are very tiny
transistors and capacitors that are switched on and off to
achieve different colors. There are rows of these TFT’s on
the screen, and each row displays a different color when
turned on. There are three colors: Red, Blue, and Green.
Remember, it’s the twisting of the crystal that actually
allows the light to bypass the crystal and become displayed.
By controlling voltage to the crystal, we can control how
much we twist it, which is used to adjust its brightness.
Most displays have 256 levels of brightness, which means the
crystals can be twisted or untwisted into 256 different
positions. By doing this, we create what they call a grey
scale. The grey scale is used to create all of our different
colors and shades we see on the monitor.
Each color has 256 different shades,
which means we can make 16.8 million different colors! To do
this, we need a large number of transistors. Depending on
the size of the screen, a typical LCD monitor uses more than
3 million transistors! One transistor bites the dust, and
WHAM – a bad pixel. This explains why it’s so common, and
why most manufacturers allow 5 or so bad pixels before they
will even warranty the unit. You also should be aware that
the larger the monitor, the bigger your chance is of having
a bad pixel. Take 1280 x 1024 and times that by 3 (the 3
different colors). You should have gotten 3,932,160, which
is a lot of transistors! The numbers are definitely not on
the LCD manufacturer’s side. It’s such a problem with larger
units that over 30% of the screens are tossed in the factory
because of irregularities.
